Many of the satellite radio transmissions by XM Radio and Sirius fail to have enough link margins for continued operations within buildings. Large metropolitan urban areas have been deployed with terrestrial repeaters to address indoor coverage problems. Unfortunately, there is no adequate approach to indoor coverage problems in rural and non-metropolitan areas.
Signals are transmitted by the satellites using a left-hand circular polarization. The antennas that receive these signals are typically designed to exploit this polarization. The first multipath reflection of a satellite signal is normally converted to right-hand circular polarization, and therefore, is not well received by the antennas. As a result, both signal strength and polarization are fighting for indoor penetration within buildings.
Current indoor reception approaches focus on directing satellite or terrestrial signals into the buildings using a repeater or sub-repeater. Two products offered by XM Radio or their affiliates address indoor coverage problems, but fall short of expectations. The first product is the Delphi Roady 2, which has a built in FM modulator to send the selected radio channel to a legacy FM radio receiver. The problem with an FM modulator is that they do not deliver adequate fidelity. The second product is the XM PCR, which receives the radio channels from the satellite or a terrestrial repeater. The XM PCR presents analog audio to the line-in of a PC audio card, and a digital data stream using a USB connection.
Currently, home or business micro-repeaters are installed in a southern window for satellite reception. Micro-repeaters need to be both a satellite receiver and a terrestrial transmitter. In these cases, they are just as complicated as a land based terrestrial macro-repeater. The micro-repeaters and macro-repeaters require a relatively large bandwidth since they relay the entire digital satellite radio channels, i.e., 100 radio channels.
For the macro-repeater, it uses a much higher gain receive antenna that can be pointed once during installation and does not need to be adjusted again. The isolation between transmit and receive frequencies can be improved by placement of the transmit and receive antennas. A very directional parabolic receive antenna with narrow beamwidth helps to eliminate the ring around problem of terrestrial transmit waveforms entering or corrupting the receive waveforms.
A micro-repeater has none of these advantages. Transmit and receive antennas are co-located in the same device. The orientation of the transmit and receive antennas should be independently adjustable. Assuming the micro-repeater can be positioned to see the southern sky, there may be less correlation to the intended indoor coverage area. Setting the digital satellite radio to receive satellite signals may not be the best setting for covering the indoor area.
The antenna on the micro-repeater is typically set once and forgotten as is the case for the macro-repeater. The isolation between transmit and receive is much less and will complicate the ring around problem. The gain on the transmit and receive antennas are again limited by size, and as such, will not have the narrow beamwidths achieved by the terrestrial macro-repeater.
Moreover, satellite radio providers have interference problems with over-deployment of terrestrial repeaters that operate in such a simulcast environment. The trend is for even more of these micro-repeaters to be scattered. This is going to worsen the interference problems.